Aspects of the invention can relate to a capacitance detection technique for reading the surface composition of an inspecting object, such as a fingerprint, having minute ridges and valleys as changes in capacitance.
With a related art fingerprint sensor, a detection circuit for reading out information of ridges and valleys of a fingerprint is formed on a single-crystalline silicon substrate. See, for example, Japanese Unexamined Patent Publication Nos. 11-118415, 2000-346608, 2001-56204, and 2001-133213. However, since a fingerprint sensor needs to have a size of around 20 mm×20 mm as required for its use, the fingerprint sensor formed on a single-crystalline silicon becomes costly. To solve this problem, a fingerprint sensor using a thin film metal-insulator-semiconductor (MIS) device has been proposed. See, for example, Japanese Unexamined Patent Publication No. 2003-254706. By using a thin film MIS device, a fingerprint sensor can also be formed on a glass substrate or a plastic substrate.